Vapor lamp power factor correction



OGL 13, 1942- G. A. FREEMAN VAPOR LAMP POWER FACTOR CORRECTION Filed May 1e, 1940 r www w ,E if h mourn. z N wnwm w mRd. Y Zw m mm m wwwa r NE R p Ww m M WNF y cl. A R .r H m M A m M 6 m Y fw B W w w u 2,298,935 VAPOR LAMP PQWER FACTOR CORRECTION George Albert Freeman,

signor to Westinghouse ing Company, East Pit tion of Pennsylvania East Orange, N. J., as- Electric & Manufacturtsburgh, Pa., a corpora- Application May 16, 1940, Serial No. 335,492

My invention relates to the circuit arrangement for discharge devices, and especially to the circuit for fluorescent lamps.

An object of my invention is to improve the v power factor of the circuit of discharge devices, especially that of fluorescent lamps.

Another object is to prevent stroboscopic effects.

Still vanother object of my invention is to simplify installations by operating two or more lamps from a single transformer.

Other objects and advantages of the invention will be apparent from the following description and drawing, in which:

Fig. 1 is a diagrammatic circuit of discharge lamps and a transformer having two high voltage secondaries.

Figs. 2 and 3 are modifications of the circuit of Fig. 1 wherein lower transformer voltages are used and special starting circuits are employed.

Fig. 4 is a graph illustrating the leading and lagging relation of the lamps in Figs. 1 through 3 and their resultant primary circuit.

One disadvantage in the use of discharge lamps such as the vapor and fluorescent types, is the inherent low power factor brought about by high voltage transformers, choke coils or reactors, which must be used to ballast or start such lamps. Power factor correction is desired especially because smaller generator and transmitting line equipment can be utilized for the power consumed. The power factor correction for such lamps, however, is applied in most transformers by a large capacity condenser shunted across an extra high voltage winding on the transformer. This involves considerable extra cost in the auxiliary equipment. If this expensive auxiliary equipment is not utilized, however, especially with lamps requiring a high starting voltage, the over all power factor is likely to be as low as 50%.

Most of these installations of lamps involve a plurality of lamps and it is one of the objects of my invention to utilize a single circuit for two or more lamps in combination and to provide a leading power factor in one branch of the circuit that will counterbalance a lagging power factor in the other branch or branches of the circuit. Because of the difference in phase, the current in two or more lamps will not pass through zero phase at the same time and accordingly there will not be a stroboscopic effect as there might be with individual installations.

In Fig. 1 I have disclosed two lamps I0 and II.

These lamps may be vapor lamps such as the 'I3 and I4 from a commercial l'Claim. (Cl. 176-124) n `high pressure mercury type or may be the fluorescent type with the interior walls of the tube coated with a fluorescent material such as willemite and made fluorescent by a discharge through the gaseous atmosphere therein which may be mercury vapor or a combination of mercury vapor with one or more of the noble gases. The tubes diagrammatically illustrated have the electrodes I2 located at opposite ends of the tube. The circuit for the lamps involves connections circuit to a transhas a single prihigh voltage secformer I5 which, in this case, mary I5 on a leg I1 and two ondaries which voltage is suilicient to start the Secondary coil I8 of leg I9 is connected lamps. to the electrodes of the tube I0 and secondary coil 20 on leg 2| is connected to the electrodes of the tube II. Magnetic shunts 22 and 23 are placed in the reactor in the two spaces between the three legs to provide leakage reactance to ballast the current. Because of the various inductances of the two branch circuits of the two lamps, the current-would normally be a lagging current in both branches. In the circuit connecting the coil I8 to the electrodes of the lamp I0, however, I insert a capacitance 24 which is preferably of such a size as to make the branch circuit of the lamp I0 leading by approximately the same value as the current through the tube II and its associated branch circuit is lagging.

In Fig. 4 I have illustrated a graph which represents the leading current of lamp I0 and the lagging current of lamp II, which in the circuit of the design results in the primary current in phase with the supply Voltage. The circuit of Fig. 1 accordingly produces a practically unity power factor.

In Fig. 2 I have illustrated a modification of this invention which is especially adapted for discharge lamps, and those utilizing a starting relay. I preferably use an auto-transformer 25 having a tap for the mid-point of its coil 26 connected to one side of an alternating current supply 21 and the opposite ends of this coil connected throughthe circuit elements hereafter described to the other side 28 of this alternating current supply. Two lamps 29 and 30 may be of the fluorescent type having electrodes 3| which are generally of an oxide coating of barium, strontium or calcium oxide, requiring a preheating before the discharge is started. In order to provide a time for the heating of these electrodes, I place in se'ries with one end of each of these electrodes a starting glow relay 32 such as described in the copending application of trodes.

' around Edward C. Dench, Ser. No. 242,927, filed Nov. 29, 1938, and now Patent 2,200,443.

This relay 32 starts with a glow discharge that heats up a 'bimetal attached to one of the 'elec- The bimetal acts tobend the electrodes into contact with each other and a current passes through the relay during which time the electrodes are heating. The bimetal cools, separating the electrodes, thus interrupting the current. This sudden interruption of the current provides a voltage kick to start the discharge in the lamp.

The other end of the electrodes is connected to the coil 26"of the auto-transformer and there is inserted in these connections a reactor 33 or 34 for current ballast.

The various inductances in the circuits will provide a lagging current through the lamps that will reduce the power factor of the lamp circuit. According to my invention, I provide a capacitance 36 in one of the branch circuits, such as that connectedto the tube 29, of sufficient size to make the power factor of the branch circuit of the tube 29 leading and preferably leading as much as the power factor of the branch circuit of the tube 'is lagging. -The capacitance reactance of 361s greater than the inductive reactance of reactor 33. The power factor of the two circuits will accordingly be practically unity, as diagrammatically illustrated in Fig. 4 previously referred to.

condenser 3B are equivalent to that of a condenser alone. This resultant condenser reactance would normally absorb the surge of an inductive kick.. The reactor 35 may be inserted in the connections between the transformer and lamp 29 to help start the lamp. When the relay 32 breaks the circuit, after a predetermined time delay, the inductive kick from reactor 35 is applied to the tube before it can be asborbed. The inductive kick will break down the path between the electrodes of lamp and start the lamp 29. Lamp 30 will be' started by the inductive kick from the transformer when the relay 32 operates.

Fig.'3 illustrates still further modification of the circuit applied to the starting circuit of two lamps 40 and 4l. 'Ihe electrodes of these two lamps are connected in series through a relay 42 which is connected a capacitor 43 to prevent radio interference when the relays 42 open after the electrodes 44 are suiciently heatcurrent ballast. A capacitance 56 is connected in the branch circuit of one of the tubes as illustrated, in order to give it a leading power factor i sufficient in value to result in unity power factor when combined with the -other branch circuit of tube 4i which has a lagging power factor.

The choke coils and transformer of Fig. 2 have been replaced by a low cost unit in Fig. 3. The reactor 35 may be added for some lamp sizes to Fig. 3 and the radio frequency condensers 43 may be added to Fig. 2.

` 30 The combined reactancesof reactor 33 and ingly,

ed and the discharge starts through the tubes. y

These lamps are energized from an auto-transformer 45 having secondary coils 46'and 41 for the My invention has a special advantage in the design and utilization of a single transformer with two secondaries. With two lamps using the condenser in one secondary circuit. the power factor will be near unity and the primary current will be less than onlin the same order as the primary current, with only one lamp burning without the condenser. Without the difference in leading and lagging power factor in the secondary circuits, the operation of two lamps on such a transformer will result in a primary current twice thatof one lamp.

My invention is, of course, applicable for installations involving more than two devices from the same transformer.- The phases in the branch circuits should be designed to produce as close as possible a substantially unity power factor in the single primary.

It is apparent that I have provided a group of discharge devices in an extremely simplified installation drawing current from a single primary and yet an installation in which substantially unity power factor and non-stroboscopic effects are produced.

While I have disclosed various combinations of branch circuits for maintaining the powerI factor in the primary practically unity, it is apparent that many other arrangements of branch circuits and elements therein may be made without departing from the spirit of the invention. Accord- Y I desire only such limitations to be imposed upon my invention as are necessitated by the spirit and-scope of the followingclaim.

I claim:

An assembly comprising a transformer, a secondary in said transformer, a discharge lamp having two filament electrodes therein, connection from said secondary toone end of each filament electrode, a starting relay, connections from said starting relay to the other ends of said filaments, said secondary circuit and discharge lamp having a leading power factor, another secondary in said transformer, another discharge lamp having two filament electrodes therein, con- ,nections from said last mentioned secondary to one end of each of said last mentioned filaments, said last mentioned secondary circuitl and discharge lamp having a lagging power factor, another starting relay and connections from said starting relay to the other ends-of the filaments of the last mentioned discharge lamp.

GEORGE ALBERT FREEMAN. 

